This invention relates in general to an electroforming process and a hollow composite article prepared by the electroforming process.
The fabrication of hollow articles by an electroforming process is well known. For example, seamless tubes may be fabricated by electrodepositing a metal or metal alloy onto a cylindrically shaped mandrel which is suspended in an electrolytic bath. The seamless electroformed tubes are thereafter removed from the mandrel by sliding the tube off one end of the mandrel. Different techniques have been developed for forming and removing tubes from electroforming mandrels depending upon the cross-sectional area of the electroformed tube. Examples of these techniques are described, for example, in U.S. Pat. No. 3,844,906 to R. E. Bailey et al and in U.S. Pat. No. 4,501,646 to W. G. Herbert.
A process for electroforming hollow nickel articles having a large cross-sectional area onto a mandrel is described in U.S. Pat. No. 3,844,906 to R. E. Bailey et al. More specifically, the process involves establishing an electroforming zone comprising a nickel anode and a cathode comprising a support mandrel, the anode and cathode being separated by a nickel sulfamate solution maintained at a temperature of from about 140.degree. F. (60.degree. C.) to 150.degree. F. (65.degree. C.) and having a current density therein ranging from about 200 to 500 amps/ft.sup.2 (20 to 50 amps/dm.sup.2) imparting sufficient agitation to the solution to continuously expose the cathode to fresh solution, maintaining this solution within the zone at a stable equilibrium composition comprising:
Total Nickel: 12.0 to 15.0 oz/gal PA0 Halide as NiX.sub.2.6 H.sub.2 O: 0.11 to 0.23 moles/gal PA0 H.sub.3 BO.sub.3 : 4.5 to 6.0 oz/gal
electrolytically removing metallic and organic impurities from the solution upon egress thereof from the electroforming zone, continuously charging to the solution about 1.0 to 2.0.times.10.sup.-4 moles of a stress reducing agent per mole of nickel electrolytically deposited from the solution, passing the solution through a filtering zone to remove any solid impurities therefrom, cooling the solution sufficiently to maintain the temperature within the electroforming zone upon recycle thereto at about 140.degree. F. (60.degree. C.) to 150.degree. F. (65.degree. C.) at the current density in the electroforming zone, and recycling the solution to the electroforming zone.
The thin flexible endless nickel belt formed by this electrolytic process is recovered by cooling the nickel coated mandrel to effect the parting of the nickel belt from the mandrel due to different respective coefficients of thermal expansion.
For metal articles fabricated by electroforming on mandrels having a small cross-sectional area, the process described in U.S. Pat. No. 4,501,646 to W. G. Herbert is preferred to overcome difficulties in removing the electroformed article from the mandrel. For example, when the chromium coated aluminum mandrel described in U.S. Pat. No. 3,844,906 is fabricated into electroforming mandrels having very small diameters of less than about 1 inch, metal articles electroformed on these very small diameter mandrels are extremely difficult or even impossible to remove from the mandrel. Attempts to remove the electroformed article can result in destruction of damage to the mandrel or the electroformed article, e.g. due to bending, scratching or denting.
Normally, hollow electroformed articles such as metal tubes are removed from one end of an electroforming mandrel and are finished by trimming each end. If the electroformed tubes are to be utilized as shafts, the ends of the tubes must normally be fitted with collets, press fit bearings or other devices which will allow the ends of the shaft to be supported by rods, bearings and the like. Although the formation of hollow members by means of electroforming is relatively economical, additional cost and manufacturing steps are required to trim the ends of the electroformed articles and to insert collets, bearings, or other support devices. Moreover, the structural strength of the resulting assembly is only as strong as the strength of the thin wall of the electroformed article.